Surface emitting lasers emit laser light in a direction perpendicular to the surface of their substrate and are expected as a light source that can be integrated (or arrayed). One such surface emitting laser is a surface emitting laser using a two-dimensional photonic crystal. A two-dimensional photonic crystal consists of a dielectric body material in which areas (“modified refractive index areas”) whose refractive index differs from that of the body material are periodically arranged. The periodic structure causes a Bragg diffraction within the two-dimensional photonic crystal and creates an energy region (“photonic band gap”) in which the transmission of light (or electromagnetic waves) is disallowed.
For example, a two-dimensional photonic crystal surface emitting laser disclosed in Patent Document 1 includes a slab-shaped two-dimensional photonic crystal located in the vicinity of an active layer which emits light when carriers are injected into it. In this two-dimensional photonic crystal, the period distance of the modified refractive index areas are determined so that it equals the wavelength that the light generated within the active layer will have within the two-dimensional photonic crystal. Therefore, a two-dimensional standing wave is created within the two-dimensional photonic crystal, whereby the light is amplified and causes a laser oscillation.
While the two-dimensional standing wave is present within the two-dimensional photonic crystal, a portion of light leaks from the lateral side of the crystal. This leads to efficiency deterioration due to the loss of energy and heat generation attributed to absorption of the leaking light by the active layer, with the result that the minimum level of current necessary for laser oscillation (i.e. the “lasing threshold”) increases.
For solving this problem, Patent Document 2 discloses a two-dimensional photonic crystal surface emitting laser including a reflector surrounding the two-dimensional photonic crystal to abate the lateral leakage of light.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-332351 (Paragraphs [0037] through [0056], FIG. 1)
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-273456 (Paragraphs [0023] through [0034], FIGS. 1 through 3)
The two-dimensional photonic crystal surface emitting laser disclosed in Patent Document 2 includes upper and lower cladding layers formed on a semiconductor substrate, an active layer sandwiched between the two cladding layers, and a two-dimensional photonic crystal located on one of the cladding layers or on the active layer. The aforementioned reflector consists of a groove extending from the upper cladding layer to the lower one, or holes functioning as a diffraction grating or two-dimensional photonic crystal.
The aforementioned groove or holes can be created by photolithography, electron-beam lithography or similar techniques. In creating the groove or holes, it is necessary to accurately control their distance from the edge of the photonic crystal because this distance significantly affects the phase of the reflected light waves; an inaccurate distance setting possibly deteriorates the device performance.